[en] We have isolated and identified three quaternary monomeric indole alkaloids from barks of Strychnos usambarensis roots. Besides Macusine B, previously found in Strychnos toxifera, two new products are described: O-methyl-macusine B and O-methyl-dihydro-macusine B. It is not easy to discuss the origin of these last products that could take formation during the extraction. The purification is very laborious because Strychnos usambarensis contains more than sixty alkaloids.